Topic
Absorption (logic)
About: Absorption (logic) is a research topic. Over the lifetime, 5733 publications have been published within this topic receiving 236302 citations.
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TL;DR: In this paper, a colloidal form of the layered semiconductor PbI was examined by transmission electron microscopy and optical absorption and it was shown that blue-shifted absorption features can be explained by carrier confinement in these differently sized crystallites, each a single layer (i.e., 12, 18, and 29 A ) with bulk symmetry.
Abstract: Microcrystallites of the layered semiconductor ${\mathrm{PbI}}_{2}$ were prepared in colloidal form and examined by transmission electron microscopy and optical absorption. The crystallites have lateral dimensions grouped around 12, 18, and 29 A\r{} corresponding to close-packed clusters with bulk ${\mathrm{PbI}}_{2}$ symmetry. Blue-shifted absorption features can be explained by carrier confinement in these differently sized crystallites, each a single layer (\ensuremath{\sim}7 A\r{}) thick.
117 citations
TL;DR: In this paper, the Mossbauer spectra and magnetization properties of single-crystalline nanostructures are reported, and the latent magnetization locked within the toroidal spin structure of nanocubes has been released.
Abstract: We report on the M\"ossbauer spectra and magnetization properties of single-crystalline ${({\text{BiFeO}}_{3})}_{x}\text{\ensuremath{-}}{({\text{BaTiO}}_{3})}_{1\ensuremath{-}x}$ solid solution nanostructures in the form of nanocubes, measuring approximately 150 to 200 nm on a side, prepared by a molten salt solid-state reaction method in the compositional range wherein $0.5\ensuremath{\le}x\ensuremath{\le}1$. Powder x-ray diffraction (XRD) and monochromatic synchrotron XRD studies indicate products of high purity, which undergo gradual, well-controlled structural transformations from rhombohedral to tetragonal structures with decreasing ``$x$.'' For all solid solution products, room-temperature magnetization studies exhibit hysteretic behavior with remnant magnetization values of ${M}_{\text{r}}\ensuremath{\ge}0.32\text{ }\text{emu}/\text{g}$, indicating that the latent magnetization locked within the toroidal spin structure of ${\text{BiFeO}}_{3}$ has been released. Room-temperature M\"ossbauer spectra show composition-dependent characteristics with decreasing magnetic hyperfine field values and increasing absorption linewidths due to a decrease in the magnetic exchange interaction strength with decreasing $x$. For the lowest $x=0.5$ composition studied, the M\"ossbauer spectra show paramagnetic behavior, indicating a N\'eel temperature for this composition below 300 K. However, room-temperature magnetization studies with applied fields of up to 50 kOe show hysteretic behavior for all compositions, including the $x=0.5$ composition, presumably due to field-induced ordering. Furthermore, hysteresis loops for all compositions exhibit smaller coercivities at 10 K than at 300 K, an observation that may suggest the presence of magnetoelectric coupling in these systems.
116 citations
TL;DR: In this paper, the Langevin-Debye formula was used to measure the paramagnetic susceptibility of conduction electron spin resonances in terms of the nuclear static susceptibility of metal nuclei in the same sample and at the same frequency, the resonance being observed merely by changing the static magnetic field.
Abstract: The paramagnetic susceptibility ${{\ensuremath{\chi}}_{p}}^{e}$ of conduction electron spins is isolated experimentally from the total magnetic susceptibility in metallic lithium and sodium by studying the intensity of the conduction-electron spin resonances. The absolute intensity of absorption is calibrated by comparison with the nuclear resonance of the metal nuclei in the same sample and at the same frequency, the two resonances being observed merely by changing the static magnetic field. In this manner ${{\ensuremath{\chi}}_{p}}^{e}$ is measured in terms of the nuclear static susceptibility, ${{\ensuremath{\chi}}_{p}}^{n}$, which in turn can be calculated accurately from the Langevin-Debye formula. A narrow band modulation technique gives improved signal to noise over our earlier work. The values of ${{\ensuremath{\chi}}_{p}}^{e}$ are (2.08\ifmmode\pm\else\textpm\fi{}0.1)\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}6}$ cgs volume units for lithium at 300\ifmmode^\circ\else\textdegree\fi{}K and (0.95\ifmmode\pm\else\textpm\fi{}0.1)\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}6}$ cgs volume units for sodium at 79\ifmmode^\circ\else\textdegree\fi{}K, in rather good agreement with the theory of Pines and Bohm, but in substantial disagreement with the simple Pauli model, or the results of Sampson and Seitz. Experimental precision does not permit conclusions to be drawn about the diamagnetism of conduction electrons.
116 citations
TL;DR: In this article, an analytical model for the spectra due to excitation of a core electron in metal with an incomplete shell was proposed. But the model assumes that the incomplete shell is treated as a nondegenerate localized state interacting with conduction band through the s − d mixing.
Abstract: Analytic features of the spectra due to excitation of a core electron in metal with an incomplete shell are studied with a simple model. The incomplete shell (denoted by d state, representatively) is treated as a nondegenerate localized state interacting with conduction band through the s – d mixing. It is assumed that in the initial state of the absorption the unoccupied d level is well above the Fermi energy e F while in the final states the d level of the excited atom is lowered down to e d due to the core hole left behind. When e d > e F , the singular absorption edge appears at \(\tilde{\varepsilon}_{\text{F}}\) as expected, with an antiresonance around \(\tilde{\varepsilon}_{d}\). When e d < e F , the singular absorption edge appears at \(\tilde{\varepsilon}_{d}\), the Fermi level threshold being blurred out by the life time effect of the d hole. Emission spectra are also calculated. The results are compared qualitatively with experimental data.
116 citations
TL;DR: In this paper, the authors derived and solved the Bethe-Salpeter ladder equation and computed the density-dependent reflectivity and absorption spectra of a ZnO single crystal at various wavelengths around the exciton resonance and in a broad carrier-density range.
Abstract: At carrier densities above the Mott density, Coulomb screening destroys the exciton resonance. This, together with band-gap renormalization and band filling, severely affects the optical spectra. We have experimentally studied these effects by ultrafast pump-probe reflectivity measurements on a ZnO single crystal at various wavelengths around the exciton resonance and in a broad carrier-density range. Theoretically, we determined the Mott density in ZnO to be $1.5\ifmmode\times\else\texttimes\fi{}{10}^{24}$ m${}^{\ensuremath{-}3}$ at 300 K. Taking a field-theoretical approach, we derived and solved the Bethe-Salpeter ladder equation and we computed the density-dependent reflectivity and absorption spectra. A carrier dynamics model has been developed, containing three-photon absorption, carrier cooling, and carrier trapping near the surface. The agreement between the theoretical reflectivity based on our model and the experimental data is excellent.
115 citations